The present invention relates to displays and, more particularly, to displays that produce images responsive to a viewer""s eye orientation.
A variety of techniques are available for providing visual displays of graphical or video images to a user. For example, cathode ray tube type displays (CRTs), such as televisions and computer monitors are very common. Such devices suffer from several limitations. For example, CRTs are bulky and consume substantial amounts of power, making them undesirable for portable or head-mounted applications.
Flat panel displays, such as liquid crystal displays and field emission displays, may be less bulky and consume less power. However, typical flat panel displays utilize screens that are several inches across. Such screens have limited use in head mounted applications or in applications where the display is intended to occupy only a small portion of a user""s field of view.
More recently, very small displays have been developed for partial or augmented view applications. In such applications, a portion of the display is positioned in the user""s field of view and presents an image that occupies a region 42 of the user""s field of view 44, as shown in FIG. 1. The user can thus see both a displayed image 46 and background information 48.
One difficulty with such displays is that, as the user""s eye moves to view various regions of the background information, the user""s field of view shifts. As the field of view shifts, the position of the region 42 changes relative to the field of view 44. This shifting may be desirable where the region 42 is intended to be fixed relative to the background information 48. However, this shifting can be undesirable in applications where the image is intended to be at a fixed location in the user""s field of view. Even if the image is intended to move within the field of view, the optics of the displaying apparatus may not provide an adequate image at all locations or orientations of the user""s pupil relative to the optics.
One example of a small display is a scanned display such as that described in U.S. Pat. No. 5,467,104 of Furness et. al., entitled VIRTUAL RETINAL DISPLAY, which is incorporated herein by reference. In scanned displays, a scanner, such as a scanning mirror or acousto-optic scanner, scans a modulated light beam onto a viewer""s retina. The scanned light enters the eye through the viewer""s pupil and is imaged onto the retina by the cornea and eye lens. As will now be described with reference to FIG. 2, such displays may have difficulty when the viewer""s eye moves.
As shown in FIG. 2, a scanned display 50 is positioned for viewing by a viewer""s eye 52. The display 50 includes four principal portions, each of which will be described in greater detail below. First, control electronics 54 provide electrical signals that control operation of the display 50 in response to an image signal VIM from an image source 56, such as a computer, television receiver, videocassette player, or similar device.
The second portion of the display 50 is a light source 57 that outputs a modulated light beam 53 having a modulation corresponding to information in the image signal VIM. The light source may be a directly modulated light emitter such as a light emitting diode (LED) or may be include a continuous light emitter indirectly modulated by an external modulator, such as an acousto-optic modulator.
The third portion of the display 50 is a scanning assembly 58 that scans the modulated beam 53 of the light source 57 through a two-dimensional scanning pattern, such as a raster pattern. One example of such a scanning assembly is a mechanically resonant scanner, such as that described U.S. Pat. No. 5,557,444 to Melville et al., entitled MINIATURE OPTICAL SCANNER FOR A TWO-AXIS SCANNING SYSTEM, which is incorporated herein by reference. However, other scanning assemblies, such as acousto-optic scanners may be used in such displays.
Optics 60 form the fourth portion of the display 50. The imaging optics 60 in the embodiment of FIG. 2 include a pair of lenses 62 and 64 that shape and focus the scanned beam 53 appropriately for viewing by the eye 52. The scanned beam 53 enters the eye 52 through a pupil 65 and strikes the retina 59. When scanned modulated light strikes the retina 59, the viewer perceives the image.
As shown in FIG. 3, the display 50 may have difficulty when the viewer looks off-axis. When the viewer""s eye 52 rotates, the viewer""s pupil 65 moves from its central position. In the rotated position all or a portion of the scanned beam 53 from the imaging optics 56 may not enter the pupil 65. Consequently, the viewer""s retina 59 does not receive all of the scanned light. The viewer thus does not perceive the entire image.
One approach to this problem described employs an optics that expand the cross-sectional area of the scanned effective beam. A portion of the expanded beam strikes the pupil 65 and is visible to the viewer. While such an approach can improve the effective viewing angle and help to ensure that the viewer perceives the scanned image, the intensity of light received by the viewer is reduced as the square of the beam radius.
A display apparatus tracks the orientation or position of a user""s eye and actively adjusts the position or orientation of an image source or manipulates an intermediate component to insure that light enters the user""s pupil or to control the perceived location of a virtual image in the user""s field of view. In one embodiment, the display includes a beam combiner that receives light from a background and light from the image source. The combined light from the combiner is received through the user""s pupil and strikes the retina. The user perceives an image that is a combination of the virtual image and the background.
In addition to the light from the background and light from the image source, additional light strikes the user""s eye. The additional light may be a portion of the light provided by the image source or may be provided by a separate light source. The additional light is preferably aligned with light from the beam combiner. Where the additional light comes from a source other than the image source, the additional light is preferably at a wavelength that is not visible.
A portion of the additional light is reflected or scattered by the user""s eye and the reflected or scattered portion depends in part upon whether the additional light enters the eye through the pupil or whether the additional light strikes the remaining area of the eye. The reflected or scattered light is then indicative of alignment of the additional light to the user""s pupil.
In one embodiment, an image field of a detector is aligned with the light exiting the beam combiner. The detector receives the reflected portion of the additional light and provides an electrical signal indicative of the amount of reflected light to a position controller.
In one embodiment, the detector is a low-resolution CCD array and the position controller includes an electronic controller and a look up table in a memory that provides adjustment data in response to the signals from the detector. Data from the look up table drives a piezoelectric positioning mechanism that is physically coupled to a substrate carrying both the detector and the image source.
When the detector indicates a shift in location of the reflected additional light, the controller accesses the look up table to retrieve positioning data. In response to the retrieved data, the piezoelectric positioning mechanism shifts the substrate to realign the image source and the detector to the pupil.
In another embodiment, the CCD array is replaced by a quadrant-type detector, including a plurality of spaced-apart detectors. The outputs of the detectors drive a control circuit that implements a search function to align the scanned beam to the pupil.
In one embodiment, imaging optics having a magnification greater than one helps to direct light from the image source and additional light to the user""s eye. Physical movement of the image source and detector causes an even greater movement of the location at which light from the image source strikes the eye. Thus, small movements induced by the piezoelectric positioning mechanism can track larger movements of the pupil position.